SMOS Data in SNAP

SMOS Data in SNAP

Representation of SMOS Data in SNAP

Metadata

The SMOS HDR product file is converted into a SNAP metadata tree.

Geo-Coding

The geo-coding of all SMOS data products is provided by the WGS-84 geographic coordinate reference system. The mapping between image pixels and SMOS grid points is established by a lookup table in form of an image of 16384 by 8192 pixels, yielding about 30 image pixels for an equatorial grid cell of the ISEA4H-R9 grid.

The lookup table was computed by means of the DGGRID software which yields a SMOS grid point sequential number seqnum for the latitude-longitude of each pixel.

The relation between the seqnum and the nominal SMOS gridPointId is given by

      int gridPointIdToSeqnum(int gridPointId) {
          return gridPointId < 1000000 ? gridPointId : gridPointId - 737856 * ((gridPointId - 1) / 1000000) + 1;
      }
  

The inversion is

      int seqnumToGridPointId(int seqnum) {
          return seqnum <= 262145 ? seqnum : seqnum == 2621442 ? 9262145 : seqnum - 1 + ((seqnum - 2) / 262144) * 737856;
      }
  

An example of the lookup table image (in lower resolution) is depicted in the image below.

Bands for Level 1C Browse - Dual Polarisation

Note that even though there are flags associated with each polarization mode all flags but those bits indicating the polarisation mode do depend on the grid cell only. Since the polarization mode is indicated by the suffix (X or Y) of the band name there is no loss of information when there is a single flag band only.

Bands for Level 1C Browse - Full Polarisation

Note that even though there are flags associated with each polarization mode all flags but those bits indicating the polarisation mode do depend on the grid cell only. Since the polarization mode is indicated by the suffix (X, Y or XY) of the band name there is no loss of information when there is a single flag band only.

Bands for Level 1C Science - Dual Polarisation

The bands in the science products are a superset of the bands in the corresponding browse products. For the browse view all bands in the science product represent measured values interpolated for an incidence angle of 42.5 degrees by means of a linear regression of all measurements at the same polarisation considering incidence angles from 37.5 to 47.5 degrees.

The HH and VV polarisations and its errors at ground are calculated by Camps et al. (2005, Eqs. 13, 14; IEEE Geoscience and Remote Sensing Letters, 1545) where the rotation of the electric fields incident in the antenna plane is given by the difference of the Faraday and geometric rotations.

Bands for Level 1C Science - Full Polarisation

The bands in the science products are a superset of the bands in the corresponding browse products. For the browse view all bands in the science product represent measured values interpolated for an incidence angle of 42.5 degrees by means of a linear regression of all measurements at the same polarisation considering incidence angles from 37.5 to 47.5 degrees.

The HH, VV, and HV polarisations and its errors at ground are calculated by Camps et al. (2005, Eqs. 13, 14; IEEE Geoscience and Remote Sensing Letters, 1545) where the rotation of the electric fields incident in the antenna plane is given by the difference of the Faraday and geometric rotations.

Level 2 User Data Products

All fields in the Ocean Salinity and Surface Moisture grid point data record are represented as bands.

Level 2 Data Analysis Products

All fields in the Ocean Salinity and Surface Moisture grid point data record that represent 2-dimensional datasets are represented as bands.

Auxiliary Data Products

Selected fields in the ECMWF, DFFLAI, DGGFLO, DGGRFI, DGGROU, DGGTFO, DGGTLV, VTEC_C, VTEC_P and LSMASK auxiliaray data products are represented as bands.